Re: CCL:colour of molecules in the solid state

Anik Peeters wrote:
>
> Dear CCLers,
>
> I am studying molecular crystals using the supermolecule approach:
> a cluster of 10-15 molecules is described by the wave function
> and this cluster is surrounded by point charges simulating the other
> neighbours. The level of theory we are using is Hartree-Fock.
>
> The molecule I am studying right now has been observed in three different
> polymorphic forms. One has a white colour, another one is yellow and a
> third one is light yellow. I have been trying to relate the yellow and
> light yellow colour to the band gap between the HOMO and LUMO.
Anik- I doubt whether the "band gap" has anything to do with the
colors
you observe. More likely they are either charge transfer transitions or
possibly Davydov splittings of the exciton states.
Before you do anything fancy why don't you visually looked at the
structures to see if there are any molecular interactions which would
suggest charge transfer transitions?
JERRY
--
**************
Jerry Perlstein
Center for Photoinduced Charge Transfer
Department of Chemistry
University of Rochester
Rochester,NY 14627-0216
Tel: (716)275-2511
FAX: (716)242-9485
perlstein # - at - # chem.chem.rochester.edu
http://www.chem.rochester.edu/~stc/perlstein.html